Granite Quarry Hydrogeologic Assessment: Minnesota
Leggette, Brashears & Graham, Inc. (LBG) was contracted to evaluate the hydrogeology and develop a long-term groundwater monitoring program at a granite quarry site in Sauk Rapids, Minnesota. The purpose of the study was to monitor groundwater levels prior to and during the quarry operations (blasting, excavating, and crushing) to identify any potential impacts to groundwater levels. LBG obtained and evaluated available geologic and hydrogeologic information relevant to the project. This information was used to develop the monitoring plan and evaluate future monitoring requirements.
To meet the objective of the evaluation, LBG completed the following tasks:
Reviewed and evaluated existing hydrogeologic data, reports, geologic and well logs;
Implemented a geographic information system (GIS) to evaluate available data;
Contacted local residents to gather information regarding their wells and request permission for short- and long-term monitoring;
Placed transducers in select residential and monitoring wells to record water levels before and during quarry operations;
Reviewed water level data relative to precipitation and quarry events;
Analyzed monthly water level measurements from select wells to identify potential impacts from quarry activities; and,
Presented findings to the planning commission and residents.
The granite in the quarry area outcrops in several locations. Where not outcropping, it is covered by as much as 25 feet of unconsolidated glacial sediment. Most residences receive their water from the unconsolidated aquifer; however, several residents receive water from deeper, granite wells. As can be expected, local residents are primarily concerned with the effect of quarry operations on their water supply.
WATER LEVEL EVALUATION
To date, it appears that quarry activities have not affected water levels in nearby wetlands, wells, or in observation wells located near the quarry. Water-level fluctuations observed can be attributed solely to precipitation events and seasonal variations. The quarry is approximately 50 feet deep; the anticipated maximum depth. Water level monitoring will continue through the duration of quarry activities, estimated to be approximately 12 to 15 years.